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Composition and size characterisation of volcanic ash
Gemma PrataSupervisors: Tamsin Mather and David Pyle
Francis et al. 2012, JGR
AndesitePollack et al. 1973
ObsidianPollack et al. 1973
1.5% Hematite dustBalkanski et al. 2007
Volcanic dust (basalt?)Volz 1973
Eyjafjallajökull, 13th May 2010
Particle size measurement
Malvern Mastersizer 2000
Size range: 0.02 – 2000 µmUses Mie and Fraunhofer scattering
Mie: requires sample refractive indexFraunhofer: refractive index not required
Need about a teaspoon of sample
Particle size distributions
0.25 2.5 25 250 25000
2
4
6
8
10
12
14VA10ETNA2001 1
VA10ETNA2001 2
VA10ETNA2001 3
VA11CHAI2008 1
VA11CHAI2008 2
VA11CHAI2008 3
VA15CHAI2008 1
VA15CHAI2008 2
VA15CHAI2008 3
VA1ASO1993 2
VA1ASO1993 4
VA1ASO1993 6
VA8EYJA2010 1
VA8EYJA2010 2
VA8EYJA2010 3Diameter (µm)
Vo
lum
e p
erc
en
tag
e (
%)
X-Ray Fluorescence(XRF)
Melt whole sample
Quench to glass
• quick and easy• bulk composition• assumes no size dependence of
composition
35 40 45 50 55 60 65 70 75 800
2
4
6
8
10
12
14
16
Total Alkalis vs. Silica DiagramIUGS classification
VA1ASO1993 VA2EYJA2010 VA3EYJA2010 VA7EYJA2010VA8EYJA2010 VA9EYJA2010 VA15-2EYJA2010 EZJEYJA2010VA4GRIM2011 VA5GRIM2011 VA6ETNA2002 VA10ETNA2001VA14ETNA2002 VA11CHAI2008 VA15CHAI2008 VA12BOINA2005VA13BOINA2005 VA16MONT1997 VA16-2TONG2012 VA17ASKJ
SiO2 (Wt%)
Na2
O +
K2O
(w
t%) Foidite
Phono-tephrite
TephriteBasanite
Tephri-phonolite
Trachy-andesite
BasalticTrachy-andesiteTrachy-
basalt
Picro-basalt
Basalt BasalticAndesite
Andesite
Trachyte
Dacite
RhyoliteTrachydacite
Phonolite
Electron Probe Microanalysis(EPMA)
• gives composition at specific points• user selects points• beam diameter 10 µm
35 40 45 50 55 60 65 70 75 800
2
4
6
8
10
12
14
16
Total Alkalis vs. Silica DiagramIUGS classification
Aso 1993 glassAso 1993 bulkEyja 2010 glassEyja 2010 bulkEtna 2001 glassEtna 2001 bulkChaiten 2008 glass (VA11)Chaiten 2008 bulk (VA11)Chaiten 2008 glass (VA15)Chaiten 2008 bulk (VA15)
SiO2 (Wt%)
Na2
O +
K2O
(w
t%)
Foidite
Phono-tephrite
TephriteBasanite
Tephri-phonolite
Phonolite
Trachy-andesite
BasalticTrachy-andesiteTrachy-
basalt
Picro-basalt
Basalt BasalticAndesite
Andesite
Trachyte
Dacite
RhyoliteTrachydacite
Glass vs. bulk composition
Colour key:Sulphates (purple)Silicates (green, blue, pink)Sulphur/sulphides (yellow, claret) Martin et al. 2008, JGR
QEMSCAN
Example from Etna 2006
Literature values compiled from Narcisi & Vezzoli, Global and Planetary Change, 1999
Complex index of refraction:n* = n + i · k
n – real partk – imaginary part
P < 0.05